The present invention relates to an image-pickup apparatus. In particular, the present invention relates to a technique for making a defect part of an image caused by a white defect signal inconspicuous or less discernible as compared with its surrounding image when the white defect signal, which is a video signal having a high signal level, is output because of a defect that has occurred in solid-state image-pickup devices used in an image-pickup apparatus.
In conventional solid-state image-pickup devices (CCDs), an abnormal dark current flows according to a pixel associated with a photoelectric conversion device because of a crystal defect of a semiconductor. Depending upon a video signal output from such a defect pixel, a video signal portion having a high signal level is obtained because of a current value of the abnormal dark current. The portion becomes higher in luminance than the surrounding image, and its white color display stands out. This results in an image display error called pixel defect (hereinafter called white defect). The white defect becomes a cause of picture quality degradation.
As a method for effecting a correction in order to make the white defect inconspicuous, there is a method of previously detecting and recording position information of a detected defect pixel and signal level information of a white defect signal output from the defect pixel, and subtracting a signal level of the white defect signal from an output video signal of a CCD prior to A-D (analog to digital) conversion on the basis of the recorded information. In this method, only the white defect signal component is subtracted. Therefore, a correction can be effected so accurately that the corrected pixel will be hardly recognizable as corrected. On the other hand, it is necessary to accurately detect the white defect signal level. For example, if the white defect signal level is varied by the temperature or the like, therefore, it is necessary to calculate a value for subtraction from a CPU on occasion according to the variation. Furthermore, the above described detection processing is conducted by digital processing, and the correction is conducted by analog processing. This results in a problem that the circuit scale for the conversion becomes large.
Furthermore, recently, an interpolation scheme for conducting both the detection processing and the correction processing in a digital section is becoming the mainstream.
It is also conceivable to substitute a signal generated by simply averaging signals supplied from pixels surrounding a defect pixel for the white defect signal supplied from the defect pixel. Such a technique is disclosed in, for example, JP-A-7-336605. In this technique, however, it is not considered whether there is spatial correlation in an image picked up according to the present inventors' view. Therefore, it is considered that the obtained effect of white defect correction is limited.